Submerged nanoporous anodized alumina structure for solar powered desalination

Abstract

Development of nano-porous structures utilizing a single step of anodization technique is well recognized as a cost-effective and straightforward approach for several applications. In the current work, anodized alumina was developed with nano-porous structure by utilizing oxalic acid as an electrolyte with a continuous voltage of 40 V. The formed nano-porous structure was subjected to desalination application because of its high absorbance of broadband solar spectrum energy. The desalination setup consists of two solar stills namely conventional and modified. The developed structure is placed in the modified still to examine its performance. It was observed that the structure distributing heat to surrounding water by absorbing photon energy from the sun through the nanopores and giving an efficient pathway to the water vapors for developing effective desalination. The nano-porous structure having ~ 45 nm average diameter. Furthermore, the band gap energy of nano-porous structure was found to be ~ 2.5 eV (Absorption Spectrum Fitting) and ~ 2.8 eV (Tauc plot). The nanoporous structure possess the visible light spectra in solar region which helps the band gaps of nanoporous structure to provide an additional supply of energy for generating more water to evaporate. Moreover, the urbach energy of the structure is 0.5 eV which reveals less defects in the modified still. The overall distillate yield of modified still was increased to 21% in contrast to conventional. Water quality analysis was also carried out before and after the desalination experiments and the results were within acceptable limits set by World Health Organization (WHO).